Spring中通过ApplicationContextAware的实现类获得的ApplicationContext是线程安全的吗？

Question

项目中我需要根据登陆用户动态修改Spring的数据源配置，即通过实现ApplicationContextAware接口来获取ApplicationContext，并将用户对应的数据源bean覆盖这个ApplicationContext的数据源bean。在多线程的情况下，是否会发生同步问题？Spring是否做到了每个线程持有独立的一份ApplicationContext，或者说我通过实现ApplicationContextAware而获得的ApplicationContext是否经过了ThreadLocal的封装优化？

Answer 1

spring-bean-3.06
AbstractBeanFactory.class@SuppressWarnings("unchecked")
protected <T> T doGetBean(final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)throws BeansException {
    final String beanName = transformedBeanName(name);
    Object bean;    // Eagerly check singleton cache for manually registered singletons.
    Object sharedInstance = getSingleton(beanName);
    // 以下省略}protected Object getSingleton(String beanName, boolean allowEarlyReference) {
        Object singletonObject = this.singletonObjects.get(beanName);
        if (singletonObject == null) {
            synchronized (this.singletonObjects) {
                singletonObject = this.earlySingletonObjects.get(beanName);
                if (singletonObject == null && allowEarlyReference) {
                    ObjectFactory singletonFactory = this.singletonFactories.get(beanName);
                    if (singletonFactory != null) {
                        singletonObject = singletonFactory.getObject();
                        this.earlySingletonObjects.put(beanName, singletonObject);
                        this.singletonFactories.remove(beanName);
                    }
                }
            }
        }
        return (singletonObject != NULL_OBJECT ? singletonObject : null);
    }单例

Answer 2

    protected Object getObjectFromFactoryBean(FactoryBean factory, String beanName, boolean shouldPostProcess) {
        if (factory.isSingleton() && containsSingleton(beanName)) {
            synchronized (getSingletonMutex()) {
                Object object = this.factoryBeanObjectCache.get(beanName);
                if (object == null) {
                    object = doGetObjectFromFactoryBean(factory, beanName, shouldPostProcess);
                    this.factoryBeanObjectCache.put(beanName, (object != null ? object : NULL_OBJECT));
                }
                return (object != NULL_OBJECT ? object : null);
            }
        }
        else {
            return doGetObjectFromFactoryBean(factory, beanName, shouldPostProcess);
        }
    }